1. Technical Field
This invention relates to a water-base ink composition, recording method for performing printing using the water-base ink composition, and recorded matter printed by that recording method. In particular, this invention relates to a water-base ink composition with excellent coloring ability, and the ink composition being capable of preventing, without degrading the glossiness of printed matter, the phenomenon where the color of a light source reflected on a chromatic color ink is different from the color of the light source (bronzing); a recording method for performing printing using the water-base ink composition; and recorded matter printed using that recording method.
2. Related Art
Water-base inks where colorants composed of dyes and pigments are dispersed in water are in use as water-base ink compositions. In these water-base inks, colorants are dispersed in water-based dispersion media using dispersants such as surfactants and fine polymer dispersants, and many proposals have been made for such ink compositions.
It is conceivable to provide, as JP-A-2004-75988 proposes, a pigment ink with excellent coloring ability and glossiness by using an aqueous dispersant of water-insoluble vinyl polymer particles. It is also conceivable to provide, as JP-A-2004-124081 proposes, a pigment ink, as a colorant, capable of printing with high print density and having excellent color tone angle dependence, by using an aqueous dispersant of water-insoluble vinyl polymer particles containing C.I. pigment blue 15:4.
Also, as an example where a titanium dioxide pigment and a pigment serving as a colorant are used in a water-base ink composition, it is conceivable to use, as JP-A-1994-287492 proposes, an ink containing titanium dioxide and carbon black and having a hydrophilic-treated surface in an inkjet printer so that stable ejection can be realized and good print density can be achieved when printing is carried out onto plain paper.
Also, it is conceivable to provide, as JP-A-2002-249685 proposes, a static image display ink containing one of yellow, magenta, cyan and black pigments, and titanium oxide as inorganic oxide so that a fine image can be formed and easily erased on a static image display screen such as a white board.
It is also conceivable to provide, as JP-A-1996-319442 proposes, an inkjet water-base ink composition containing particles (titanium oxide, etc.) having no effect on a required recording color so that, when the ink is provided on a recording medium, or when fixation treatment is performed, or when cleaning treatment is performed, a clear image can be formed with only a small degree of smearing of the ink on the recording medium.
It is also conceivable to provide, as JP-A-2005-179482 proposes, a water-base ink composition prepared so that the weight ratio between titanium dioxide and a chromatic color pigment is 0.6 or greater to prevent bronzing and flip-flop.
In the meantime, conventional water-base ink compositions containing titanium dioxide pigments still have room for improvement regarding the prevention of bronzing. Bronzing notably occurs with cyan ink compositions in particular and there has been a desire for its prevention.
However, although the water-base ink compositions using aqueous dispersants described in the foregoing JP-A-2004-75988 and JP-A-2004-124081 have excellent coloring abilities, they cannot prevent bronzing sufficiently. Moreover, none of the foregoing JP-A-1994-287492, JP-A-2002-249685, or JP-A-1996-319442 discloses or mentions bronzing. Furthermore, although the water-base ink composition disclosed in JP-A-2005-179482 can prevent bronzing, there are cases where the glossiness of printed matter degrades as the concentration of titanium dioxide in the water-base ink composition increases. In other words, when the concentration of a chromatic color pigment increases, it becomes necessary to increase the concentration of titanium oxide in order to prevent bronzing, and, as a result, when the content of a chromatic color pigment exceeds 3 wt. %, the glossiness of printed matter degrades remarkably due to the increased titanium dioxide. Also, the increase in the concentration of titanium dioxide causes clogging of nozzles in inkjet printers and sometimes causes cohesion of dispersed resins, and so also degrades glossiness.